A transfer printing film for transfer printing patterns comprising any combination of logo, words, numbers, etc. on pattern receive surfaces, such as surfaces of plastic articles and the like, generally includes a strip-shaped substrate film and an ink layer disposed on one side of the substrate film so as to form the pattern by means of gravure or screen printing. In the operation of applying pattern to article, the transfer printing film is so placed that the pattern thereof is positioned in a predetermined printing area of a surface of the article, and the film is sandwiched between a thermal pad and the article under a certain pressure, whereby the heated ink layer is transferred from the substrate film to the article.
In case of printing patterns on golf balls, taking into consideration how they are used, it is particularly desired that transferred ink layer is hardly removed.
Generally, the golf balls are, after the pattern is printed, subjected to urethane finish, which is substantially carried out by spraying a two-component urethane paint or two-pack urethane paint, to form a clear top coat covering the golf ball and the printed pattern in order to improve appearance of them as well as to protect them from dirt, scratch, etc. However, when an adhesion between the urethane layer of the finish coat and the ink layer of the printed pattern is weak, the ink layer tends to be easily removed.
In order to enhance the adhesion between the two layers, a transfer printing film is disclosed in Japanese Unexamined Patent Publication No.89214/95, that a urethane resin having a desired hydroxyl value is incorporated in the ink. Accordingly, when spraying the two-component urethane paint to the golf ball, the hydroxyl-functional urethane resin in the ink layer, which has been already transferred to the surface of the golf ball, reacts with the isocyanate functional resins existing in one of the two components of the paint to form urethane bondings. As a result strong chemical cross links and adhesion between the urethane finish layer and the ink layer are realised.
On the other hand, it is known to the art that a lower transfer temperature is preferable because a higher one costs more thermal energy as well as it may give rise to a heat damage of the article, the damage of distortion of dimples or golf ball itself in case the article is a golf ball, for example. The higher transfer temperature may also tend to cause a shrinkage of the substrate film consisting of synthetic resin such as polypropylene and the like, and the shrinkage of the substrate film further causes a crease or a distortion of pattern transferred to the surface of article. In this aspect, the transfer printing film according to the above-mentioned Patent Publication has a drawback that it is likely to need essentially a higher transfer temperature, for the ink layer of which comprises as a main vehicle urethane resin whose softening temperature is relatively high. In fact, the Publication teaches that the transfer temperature required in the operation using the above transfer printing film is about 130.degree. C.